1. Field of the Invention
The present invention relates to a stator in which one side of each of a plurality of coils wound in advance is inserted in the slot of its core and then the other side of each of the plurality of coils is inserted in another slot and the coils overlap each other in a spiral when viewed from the end surface of the stator core.
2. Description of the Related Art
As the manufacturing method of a stator with a wound coil, a direct winding method of winding in series a coil wound around the inner teeth of the stator core and a coil insertion method of inserting a coil wounded in advance in the slot of the stator core are mainly known.
However, since these methods can form only a coil in which each magnetic pole is concentrically wound, a motor using such a stator core causes torque unevenness due to a phenomenon that the magnetic force generation density in a running direction becomes uneven. Since this torque unevenness makes the motor vibrate or cause noise, various methods are proposed in order to solve this problem.
As a motor whose torque unevenness is remarkably reduced, a motor using a stator in which after one side of each of a plurality of coils wound in advance is inserted in the slot of its core, the other side of each of the plurality of coils is inserted in another slot and when viewed from the end surface of the stator core the coils overlap each other in a spiral (hereinafter called “spirally coiled stator”) is known.
The stator obtained thus has a short coil end and a fairly uniform compact height. Simultaneously, since its torque unevenness is small when used for a motor, the vibration and noise of the motor can be reduced.
However, in the above-described spirally coiled stator, each of both sides of a coil must be inserted in a slot while overlapping it on another coil and it is difficult to mechanize the work. Therefore, since a coil wound in advance must be manually inserted in the slot of the stator core, its manufacturing workability is low and its manufacturing costs becomes high.
As the technology concerning the above-described spirally coiled stator, Patent Document 1 of Japanese Patent Application Publication No. S56-41736 discloses the manufacturing method of a multiphase armature coil featured by consecutively winding so as to accommodate a plurality of adjacent pole same-phase coils in every another slot using a two-layered multiphase armature coil having less than one of slot per each pole per phase and then performing the same two-layer winding using the remaining slots (see FIG. 4 of the Patent Application Publication No. S56-41736).
Patent Document 2 of Japanese Patent Application Publication No. H10-28346 discloses a brushless DC motor in which two-step winding is applied to the inner teeth of one slot of a stator and one-step winding is applied to every another slot (see FIG. 1 of the Patent Application Publication No. H10-28346).
However, the above-described Patent Documents 1 and 2 do not disclose a method for mechanizing the work of inserting a wound coil in the slot of the stator core. Therefore, the coil must be manually inserted, a motor cannot be manufactured industrially in low costs and in high coil occupancy.